Magnetic media are used in various electronic devices such as hard disk drives and magnetoresistive random access memory (MRAM) devices. Hard-disk drives are the storage medium of choice for computers and related devices. They are found in most desktop and laptop computers, and may also be found in a number of consumer electronic devices, such as media recorders and players, and instruments for collecting and recording data. Hard-disk drives are also deployed in arrays for network storage. MRAM devices are used in various non-volatile memory devices, such as flash drives and dynamic random access memory (DRAM) devices.
Magnetic media devices store and retrieve information using magnetic fields. The disk in a hard-disk drive is configured with magnetic domains that are separately addressable by a magnetic head. The magnetic head moves into proximity with a magnetic domain and alters the magnetic properties of the domain to record information. To recover the recorded information, the magnetic head moves into proximity with the domain and detects the magnetic properties of the domain. The magnetic properties of the domain are generally interpreted as corresponding to one of two possible states, the “0” state and the “1” state. In this way, digital information may be recorded on the magnetic medium and recovered thereafter.
Magnetic storage media typically comprise a non-magnetic glass, composite glass/ceramic, or metal substrate with a magnetically susceptible material between about 100 nm and about 1 μm thick deposited thereon by a deposition process, commonly a PVD or CVD process. In one process, a layer comprising cobalt and platinum is sputter deposited on a structural substrate to form a magnetically active layer. The magnetically susceptible layer is generally either deposited to form a pattern, or is patterned after deposition, such that the surface of the device has areas of magnetic susceptibility interspersed with areas of magnetic inactivity denominated by orientation of their quantum spin. Where domains with different spin orientations meet, there is a region referred to as a Bloch wall in which the spin orientation goes through a transition from the first orientation to the second. The width of this transition region limits the areal density of information storage because the Bloch wall occupies an increasing portion of the total magnetic domain.
To overcome the limit due to Bloch wall width in continuous magnetic thin films, the domains can be physically separated by a non-magnetic region (which can be narrower than the width of a Bloch wall in a continuous magnetic thin film). Conventional approaches for creating discrete magnetic and non-magnetic areas on a medium have focused on forming single bit magnetic domains that are completely separate from each other, either by depositing the magnetic domains as separate islands or by removing material from a continuous magnetic film to physically separate the magnetic domains. A patterned mask may be applied to a non-magnetic substrate, and a magnetic material deposited over exposed portions of the non-magnetic substrate, or the magnetic material may be deposited before masking and patterning, and then etched away in exposed portions. By one method, the non-magnetic substrate is topographically patterned by etching or scribing, and the magnetically susceptible material deposited by spin-coating or electroplating. The disk is then polished or planarized to expose the non-magnetic boundaries around the magnetic domains. In some cases, the magnetic material is deposited in a patterned way to form magnetic grains or dots separated by a non-magnetic area.
Such methods are expected to yield storage structures capable of supporting data density up to about 1 TB/in2, with individual domains having dimensions as small as 20 nm. All such methods typically result in significant surface roughness of the medium. Altering the topography of the substrate can become limiting because the read-write head of a typical hard-disk drive may fly as close as 2 nm from the surface of the disk. Thus, there is a need for a process or method of patterning magnetic media that has high resolution and does not alter the topography of the media, and an apparatus for performing the process or method efficiently for high volume manufacturing.